Optical system for deflecting image

ABSTRACT

An optical system for deflecting an image by decentering a portion of a photographic lens in a direction perpendicular to an optical axis, wherein the decentering aberrations produced by the decentering are reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to image stabilizing photographic optical systems.

2. Description of the Related Art

In shooting the camera while riding on a moving motor vehicle such as a car or aircraft, vibrations propagates to the photographic system, thereby resulting in a blurred image at the focal plane. In this case, the distance the image shifts from the intended location in the picture frame increases as the focal length of the photographic system increases.

A method of avoiding such image shift has been proposed in the stabilized optical systems of, for example, Japanese Pat. Publications Nos. Sho 56-34847, 57-7414 and 57-7416.

The common method employed in these documents is that an optical member constituting part of the photographic system is freely suspended in space to generate a prism whose wedge angle varies with angular deviation of the camera from the intended line of sight so that the rays of light deflected by the prism provide a stationary image on the focal plane.

Meanwhile, U.S. patent applications Ser. Nos. 896,639, 116,668 and 116,541, now U.S. Pat. No. 4,844,602, disclose a technique that accidental motion of the photographic optical system is detected by utilizing, for example, an acceleration sensor. Responsive to the thus-obtained signal, an actuator oscillates a lens unit constituting part of the photographic system in a direction perpendicular to the optical axis to stabilize the image against such motion. As this actuator use may be made of a solenoid or a laminated assembly of piezoelectric elements.

It is also possible to use an image sensor such as CCD. Motion of the image formed on the CCD is analyzed through an electrical signal processing system. The thus-obtained signal may be used to obtain the stationary image at the focal plane.

In order that the photographic lens system is partly operated by means of the actuator in the manner described above to compensate for image movement to obtain the stationary image, the operating mechanisms are generally required to get a good responsiveness.

For this reason, the lens unit movable for image stabilization should be as far reduced in size and weight as possible, and the inertial mass be minimized. Further, tee relationship between the accidental displacement of the camera and the required amount of movement of that lens unit for compensating for the image movement is simplified with an advantage of shortening the computing time for conversion. Hence, the photographic lens system must be designed in such a way as to fulfill these requirements.

In addition thereto, because the movable lens unit when decentered produces decentering coma, decentering astigmatism, decentering chromatic aberrations and other decentering aberrations, it becomes difficult to preserve good optical performance against accidental displacement of the camera.

SUMMARY OF THE INVENTION

A first object of the invention has its concern with decentering a portion of a photographic lens from an optical axis of the lens to stabilize an image at the focal plane, an is to achieve a minimization of the size of that movable portion or lens unit.

A second object is to provide a photographic optical system which has, despite the decentering of the portion of the photographic lens, to be able to preserve good optical performance.

A third object is to lessen the decentering aberrations throughout the entire decentering range.

A fourth object is to provide a stabilized photographic lens of long focal length, while lessening the decentering chromatic aberrations which would otherwise extremely be increased particularly when the focal length increases.

A fifth object is to provide a photographic lens which enables good stability of optical performance to be achieved throughout the decentering range in such a manner that the remarkably large variation with decentering of illumination in the corners of the picture frame, as it would be, is limited to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3, 7, 9, 11, 13 and 15 are longitudinal section views of numerical examples 1, 2, 3, 4, 5, 6, 7 and 8 of specific lenses respectively.

FIGS. 4(A) and 4(B), 5(A) and 5(B), 6(A) and 6(B), 8(A) and 8(B), 10(A) and 10(B) 12(A) and 12(B), 14(A) and 14(B), and 16(A) and 16(B) are graphic representations of the aberrations of the numerical examples 1, 2, 3, 4, 5, 6, 7 and 8 of lenses according to the invention respectively.

In these graphs, the aberrations with the movable lens unit before being decentered are illustrated in FIGS. 4(A), 5(A), 6(A), 8(A). 10(A), 12(A), 14(A) and 16(A), and the aberrations with the movable lens unit after decentered 2 mm in parallel are illustrated in FIGS. 4(B), 5(B), 6(B), 8(B), 10(B), 2(B), 14(B) and 16(B). Also, the image height is denoted by Y, the meridional image surface by M, the sagittal image surface by S, and the aberration curves for the spectral d-line and g-line are labeled d and g respectively.

FIG. 17 is a schematic diagram of another embodiment of the operating mechanism for the optical system according to the invention.

FIGS. 18(A) and 18(B) are diagrams of geometry taken to explain how the rays of light change their positions when only the movable lens unit is moved out of axial alignment of the photographic lens.

FIG. 19 is a graph of the illumination intensity distribution over the image height for the case of FIG. 18(A).

FIG. 20 is a graph of the illumination intensity distribution for the case of FIG. 18(B).

FIG. 21 i aberration curves with respect to 18(A).

FIG. 22 is aberration curves with respect to FIG. 18(B).

FIG. 23 is a plan view of a practical example of a light beam limiting member of the invention.

FIG. 24 is a graph of the illumination intensity distribution to FIG. 17.

FIG. 25 is aberration curves with respect to FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To begin with, before embarking on description of the embodiments of the invention, what decentering aberration is produced when the movable lens unit is moved in a direction perpendicular to the optical axis to compensate for the image shift is explained from the standpoint of the aberration theory Matsui presented to the 23rd Applied Physics Lecture Meeting (in the year of 1962). According to this theory, when the photographic lens is partly parallel-decentered from the optical axis by a decentering distance E, the resultant amount of aberrations Δ'Y of the entire lens system is given by the expression of the sum of the amount of aberrations ΔY generated before the decentering and the amount of aberrations ΔY(E) produced by the decentering, i.e., an equation (a):

    Δ'Y=ΔY+ΔY(E)                             (a)

Hence, having developed a theorem from this equation, the inventors have found the expression of the decentering aberration amount ΔY(E) in terms of the primary decentering coma (IIE), the primary decentering astigmatism (IIIE), the primary decentering field curvature (PE), the primary distortion (VE1), the primary decentering distortion surplus aberration (VE2), the secondary decentering astigmatism (IIIE²), the secondary decentering field curvature (PE²), the secondary decentering distortion (VE² 1), the secondary distortion surplus aberration (VE² 2), the primary original point shift (ΔE) and the tertiary original point shift (ΔE³), by the following equation (b): ##EQU1##

In a photographic lens comprising a movable lens unit made to parallel-decenter and a fixed lens unit, where α_(P), and α'_(P) represent the incident angle and the exit angle, respectively, of the paraxial ray of light in the movable lens unit when the focal length of the entire lens system is normalized to be "1", and α_(P) represents the incident angle of the principal ray of the off-axial light, all the above-cited aberrations are expressed in terms of the aberration coefficients I_(P), II_(P), III_(P), P_(P) and V_(P) of the movable lens unit by the following equations (c) to (m): ##EQU2##

From these equations, it is concluded that in order to achieve minimization of the produced amount of decentering aberrations, it is necessary either to make small the value of each of all the aberration coefficients I_(P), II_(P), III_(P), P_(P) and V_(P) of the movable lens unit, or to determine the values of all the aberration coefficients in good balance so that they cancel one another as will be seen from the equations (b) to (k). And, in the movable lens unit itself, not only the spherical aberration, coma and Petzval sum, but also the astigmatism and distortion must be corrected well.

The present invention is next described in connection with embodiments thereof.

Referring to FIGS. 1, 2 and 3, an embodiment of the stabilized photographic lens according to the invention is shown, comprising a front lens unit I which is stationary in a direction perpendicular to an optical axis of the lens, and a rear lens unit II which is movable in the direction perpendicular to the optical axis for compensating for the image blur and has a plurality of lens elements. F denotes a focusing lens arranged to axially move. An operating mechanism for the movable lens unit II comprises an acceleration detecting device A for determining the accidental displacement of the whole lens system, in other words, the degree of blurring shift of the image at the focal plane, and driving means B responsive to the output of the acceleration detecting device A for moving the movable lens unit II in either direction indicated by the arrows to stabilize the image against the accidental displacement.

To correct the movable lens unit II for longitudinal and lateral aberrations both in good balance, it must generally be designed in such a way that the height h of the on-axial ray and the height e of the principal one of the off-axial rays in the interior of the movable lens unit take different values from each other.

From this reason, in this embodiment, to minimize the produced amount of decentering aberrations, the movable lens unit II is made up from a plurality of lenses, and the following condition is set forth

    0.05<L.sub.2 /F<0.4                                        (1)

where L₂ is the length from the frontmost to the rearmost lens surface of the movable lens unit, and F is the focal length of the entire lens system.

When the overall thickness of the movable lens unit is shorter than the lower limit of the inequalities of condition (1), the height h of the on-axial ray and the height h of the principal, off-axial ray come to approach the same value at each lens surface in the movable lens unit. Thus, the movable lens unit becomes more difficult to correct for minimization o spherical aberration, coma, astigmatism and distortion at once. Also, the produced amount of decentering aberrations is increased objectionably.

When the upper limit is exceeded, the diameter of the rear lens in the movable lens unit is caused to increase largely. Along with this, the weight, also increases. Therefore, this is undesirable as the load on the actuator for driving the movable lens becomes too large Also, the lens system as a whole is increased in size objectionably.

In this embodiment, by satisfying all the above-described features, a photographic lens of lessened decentering aberrations for good optical performance is realized. Yet, to reduce the necessary number of constituent lenses of the movable lens unit as far as possible in such a manner that the produced amount of decentering aberrations is as far lessened as possible, the movable lens unit is preferably divided by a longest air separation as the boundary into two parts of which the front is called a "front lens sub-unit IIA" and the rear a "rear lens sub-unit IIB", with the air separation D_(max) ' the refractive power φ_(II) of the movable lens unit and the refractive power φ_(IIB) of the rear lens sub-unit satisfying the following conditions:

    0.05<D.sub.max ·φ.sub.II <0.6                 (2)

    0.4<φ.sub.IIB /φ.sub.II <2                         (3)

The inequalities of conditions (2) and (3) in combination give proper ranges for the air separation and the refractive power of the rear lens sub-unit as the movable lens unit is divided into the front and rear lens sub-units to lessen mainly the produced amount of decentering aberrations.

When the air separation is too narrow or the refractive power of the rear lens sub-unit is too weak as exceeding the lower limit of the condition (2) or (3) respectively, the difficulty of fulfilling the requirements of reducing the number of lenses and of lessening the produced amount of decentering aberrations increases. Also, the distortion of the entire lens system tends to be over-corrected.

When the upper limit of each of the conditions (2) and (3) is exceeded, the weight of the movable lens unit, or the load on the actuator, is increased objectionably. Also, this leads to an increase in the size of the entire lens system too.

Still another feature of the present embodiment is to correct the movable lens unit in itself for spherical aberration, coma and other normal aberrations by setting forth the following condition:

    0.1<R.sub.IIa /F<0.6                                       (4)

where R_(IIa) is the radius of curvature of the frontmost lens surface of the movable lens unit.

The inequalities of condition (4) are to admit of constructing the movable lens unit with as few a number of lenses as possible but to allow for correction of all aberrations in good balance. When the curvature of that lens surface is weakened as exceeding the upper limit, it becomes difficult to correct the spherical aberration and coma in the movable lens unit. Also, when the movable lens unit is decentered to compensate for the image blur, large decentering coma, astigmatism, etc. are produced.

When the curvature is too strong beyond the lower limit of the condition (4), that lens surface produces large spherical aberration and coma, and the variation of aberrations with decentering of the movable lens unit is increased objectionably.

For numerical examples 1 and 2 shown in FIGS. 1 and 2 respectively, the front lens sub-unit is constructed from a positive lens whose front surface has a stronger convex curvature than the rear surface has, and a negative lens in bi-concave form, and the rear lens sub-unit is constructed from two positive lenses each in bi-convex form.

For another numerical example 3 shown in FIG. 3, the front lens sub-unit is constructed from two positive lenses and one negative lens in bi-concave form, and the rear lens sub-unit is constructed from one positive lens in bi-convex form.

By using such a construction and arrangement and such forms, a minimization of the amount of produced decentering aberration is achieved. It is also to be noted that in the examples 1, 2 and 3, a lens unit F of negative power in the fixed lens unit is moved rearward to effect focusing down from infinity to the minimum object distance.

It should be noted in connection with this embodiment that the use of at least one aspherical surface in the movable lens unit will facilitate improvement of the aberration correction and simplification of the lens structure. In this case, the aspherical surface, if of convex form, is preferably so figured that when in application to the front lens sub-unit, the radius of curvature becomes progressively larger toward the margin of the lens, or when to the rear lens sub-unit, the radius of curvature becomes progressively smaller toward the margin. For a concave aspherical surface, the figuring of the radius of curvature is preferably reversed.

In this embodiment, even if a filter or a lens unit of strong power is positioned behind the movable lens unit, the objects of the invention can be accomplished with similar advantages to those described above.

Also, though the foregoing illustrated embodiment has been described in connection with the parallel decentering of the movable lens unit for image stabilization, the movable lens unit may otherwise be tilted to effect an equivalent result in obtaining the prescribed optical performance.

It should be noted that the lens employed in the numerical examples of the invention is of the mono-focal length type, ut may be a zoom lens without disadvantages at all. In the latter case, the focal length so far termed F for the lens of the invention should be taken at the value for the telephoto end.

The numerical data in accordance with which the examples 1 to 3 of the invention can be constructed are shown in the following tables for the radii of curvature, R, the axial thicknesses or air separations, D, and the refractive indices, N, and Abbe numbers, ν, of the glasses of the lenses with the subscription numbered from front to rear.

    __________________________________________________________________________     Numerical Example 1 (FIGS. 1, 4(A) and 4(B)):                                  F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 113.55                                                                             D1 = 19.44                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -334.36                                                                            D2 = 1.23                                                             R3 = 110.16                                                                             D3 = 17.91                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -280.81                                                                            D4 = 0.43                                                             R5 = -258.76                                                                            D5 = 5.63                                                                              N3 = 1.80610                                                                            ν3 = 40.9                                         R6 = 373.36                                                                             D6 = 17.98                                                            R7 = 53.56                                                                              D7 = 6.14                                                                              N4 = 1.58913                                                                            ν4 = 61.0                                   I     R8 = 44.62                                                                              D8 = 22.54                                                            R9 = -200.53                                                                            D9 = 6.14                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -73.08                                                                            D10 = 2.56                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 94.71                                                                             D11 =  31.38                                                          R12 = 867.04                                                                            D12 = 5.93                                                                             N7 = 1.69895                                                                            ν7 = 30.1                                         R13 = -79.27                                                                            D13 = 2.56                                                                             N8 = 1.80610                                                                            ν8 = 40.9                                         R14 = 217.33                                                                            D14 = 11.46                                                           R15 = 58.70                                                                             D15 = 5.83                                                                             N9 = 1.61800                                                                            ν9 = 63.4                                         R16 = 399.79                                                                            D16 = 13.25                                                           R17 = -161.69                                                                           D17 = 1.84                                                                             N10 = 1.59270                                                                           ν10 = 35.3                                        R18 = 63.64                                                                             D18 = 21.65                                                     II    R19 = 325.29                                                                            D19 = 5.12                                                                             N11 = 1.60729                                                                           ν11 = 59.4                                        R20 = -151.28                                                                           D20 = 7.34                                                            R21 = 145.64                                                                            D21 = 5.12                                                                             N12 = 1.61800                                                                           ν12 = 63.4                                        R22 = -503.84                                                            __________________________________________________________________________

    __________________________________________________________________________     Numerical Example 2 (FIGS. 2, 5(A) and 5(B)):                                  F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 105.55                                                                             D1 = 18.85                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -471.95                                                                            D2 = 1.22                                                             R3 = 104.11                                                                             D3 = 16.30                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -623.40                                                                            D4 = 4.21                                                             R5 = -339.19                                                                            D5 = 5.60                                                                              N3 = 1.72047                                                                            ν3 = 34.7                                         R6 = 257.20                                                                             D6 = 15.28                                                            R7 = 52.16                                                                              D7 = 6.11                                                                              N4 = 1.58913                                                                            ν4 = 61.0                                   I     R8 = 43.31                                                                              D8 = 31.15                                                            R9 = -185.15                                                                            D9 = 6.11                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -61.14                                                                            D10 = 2.55                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 86.48                                                                             D11 = 28.21                                                           R12 = 573.71                                                                            D12 = 6.42                                                                             N7 = 1.59270                                                                            ν7 = 35.3                                         R13 = -53.11                                                                            D13 = 2.55                                                                             N8 = 1.77250                                                                            ν8 = 49.6                                         R14 = 270.99                                                                            D14 = 11.67                                                           R15 = 48.54                                                                             D15 = 6.62                                                                             N9 = 1.61800                                                                            ν9 = 63.4                                         R16 = 646.86                                                                            D16 = 10.22                                                           R17 = -155.78                                                                           D17 = 2.55                                                                             N10 = 1.72047                                                                           ν10 = 34.7                                        R18 = 54.73                                                                             D18 = 19.21                                                     II    R19 = 251.70                                                                            D19 = 5.60                                                                             N11 = 1.60311                                                                           ν11 = 60.7                                        R20 = -117.86                                                                           D20 = 4.95                                                            R21 = 110.83                                                                            D21 = 5.60                                                                             N12 = 1.61800                                                                           ν12 = 63.4                                        R22 = -785.11                                                            __________________________________________________________________________

    __________________________________________________________________________     Numerical Example 3 (FIGS. 3, 6(A) and 6(B)):                                  F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 100.045                                                                            D1 = 17.90                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -808.652                                                                           D2 = 1.23                                                             R3 = 108.837                                                                            D3 = 16.37                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -382.854                                                                           D4 = 2.74                                                             R5 = -306.302                                                                           D5 = 5.63                                                                              N3 = 1.80610                                                                            ν3 = 40.9                                         R6 = 360.823                                                                            D6 = 12.77                                                            R7 = 53.207                                                                             D7 = 6.14                                                                              N4 = 1.58913                                                                            ν4 = 61.0                                         R8 = 42.716                                                                             D8 = 34.49                                                      I     R9 = -241.544                                                                           D9 = 6.14                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -78.521                                                                           D10 = 2.56                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 89.435                                                                            D11 = 30.43                                                           R12 = -322.620                                                                          D12 = 5.42                                                                             N7 = 1.69895                                                                            ν7 = 30.1                                         R13 = -57.304                                                                           D13 = 2.56                                                                             N8 = 1.77250                                                                            ν8 = 37.4                                         R14 = 1464.781                                                                          D14 = 11.38                                                           R15 = 54.725                                                                            D15 = 6.65                                                                             N9 = 1.61800                                                                            ν9 = 68.3                                         R16 = 1743.956                                                                          D16 = 0.10                                                            R17 = 67.106                                                                            D17 = 3.68                                                                             N10 = 1.48749                                                                           ν10 = 70.2                                        R18 = 179.042                                                                           D18 = 5.84                                                            R19 = -325.511                                                                          D19 = 2.05                                                                             N11 = 1.60342                                                                           ν11 = 38.0                                        R20 = 41.901                                                                            D20 = 38.64                                                     II    R21 = 130.270                                                                           D21 = 5.63                                                                             N12 = 1.60729                                                                           ν12 = 47.2                                        R22 = -159.288                                                                          D22 = 10.23                                                           R23 = ∞                                                                           D23 = 2.05                                                                             N13 = 1.51633                                                                           ν13 = 64.1                                        R24 = ∞                                                            __________________________________________________________________________

Referring next to FIGS. 7, 9 and 11, there is shown another embodiment of the invention in which, despite a further reduction of the size of the movable lens unit, high grade optical performance is maintained stable against decentering.

In this embodiment, the photographic lens comprises, from front to rear, a fixed lens unit I in relation to the direction perpendicular to the optical axis, and a movable lens unit V for compensating for the image blur as it moves in a direction perpendicular to the optical axis wherein the focal length of the movable lens unit υ is represented by Fυ and the lens length is represented by L2. The movable lens unit V having a positive first lens, a negative second lens whose front surface has a stronger refracting power in negative sense than the rear surface, and a lens sub-unit including at least one positive lens and whose overall refractive power is positive, wherein letting the focal length of the entire system be denoted by F, the air separation between the first and second lenses by DV₁₂, and the shape parameters of the first and second lenses by SV₁ and SV₂ respectively where the equation for a shape parameter S is S=(RB+RA)/(RB-RA) wherein RA and RB represent the radii of curvature of the front and rear surfaces respectively, the following conditions are satisfied:

    0.05<L2/F<0.2                                              (5)

    -2<SV.sub.1 <1                                             (6)

    0<SV.sub.2 <5                                              (7)

    0.01<DV.sub.12 /FV<0.08                                    (8)

The technical significance of each of these conditions is next explained.

The inequalities of condition (5) represent a range for the total length of the movable lens unit to achieve the desired reduction of the bulk and size of the movable lens unit while still permitting variation of decentering coma, decentering astigmatism, decentering field curvature and decentering distortion to be entirely limited to a minimum when the image blur is compensated for. With a particular emphasis on minimization of, for example, the decentering distortion produced, it is in the general case that the movable lens unit must be corrected as a whole for small Petzval sum and astigmatism. From this reason, in this embodiment, the heights of the on-axial and off-axial rays of light are made different from each other in the interior of the movable lens unit. By this, the Petzval sum and astigmatism are corrected well.

When the total length of the movable lens unit is too short as exceeding the lower limit of the condition (5), it becomes difficult to minimize variation of distortion with decentering. When it is too long beyond the upper limit, the diameter of the rear members of the movable lens unit is caused to increase. This leads not only to an increase in the bulk and size of the movable lens unit and the weight of the mounting therefor, but also to increase the stress on the actuator. Therefore, the responsiveness is lowered objectionably.

The factors in the conditions (6) and (7) represent the shapes o the first and second lenses. Particularly the convex curvature of the front surface of the first lens is not made so much small, and the front surface of the second lens, too, which has a strong refracting power, is given so appropriate a concave curvature, that the chief aim to achieve the minimization of the size of the movable lens unit in such a manner as to produce astigmatism, decentering coma, decentering distortion, etc. at minimum, is accomplished.

When the radius of curvature of the convex front surface of the first lens is too small as exceeding

the upper limit of the condition (6), it produces large astigmatism. When the tendency to the rearward convexity of the second lens is stronger than the upper limit of the condition (7), the amount of astigmatism produced toward over-correction for the compensating purpose is decreased. In either case, under-correction of the astigmatism of the movable lens unit results, and the size of the movable lens unit becomes difficult to minimize.

Meanwhile, when the lower limits of the conditions (6) and (7) are exceeded, the tendency to correct astigmatism is changed from the under-correction to the over-correction. By this, it is made easier to correct the decentering distortion well. However, the tendency to direct the shaping of the first lens to rearward convexity is intensified. Therefore, large under-correction of third-order spherical aberration results. Also, as the radius of curvature of the concave front surface of the second lens becomes too small, large over-correction of higher order spherical aberration results. Thus, it becomes difficult to achieve the minimization of the total length of the movable lens unit in such a manner as to well correct spherical aberration, decentering coma. etc.

The inequalities of condition (8) represent a range for the air separation between the first and second lenses to well correct mainly the coma of the entire lens system, and particularly flare of the upper marginal rays, and to minimize the diameter of the rear members of the movable lens unit. When the air separation is wider than the upper limit, the upward coma and particularly the coma flare of the upper marginal rays are increased largely. To correct these well, the number of lenses of the movable lens unit must be increased.

When the air separation is too narrow as exceeding the lower limit, it becomes impossible to assure a sufficient refractive power for the air lens formed by the rear lens surface of the first lens and the front lens surface of the second lens. Therefore, correction of spherical aberration becomes difficult.

In this embodiment, by satisfying the above-described various conditions, a photographic lens of minimized decentering aberration for good optical performance is achieved. Yet, to reduce the range of variation of aberrations with decentering with the limitation of the number of lens elements of the movable lens unit to a minimum, the above-described lens sub-unit includes at least two positive lenses, and satisfies the following condition:

    -5<SV.sub.31 <-0.5                                         (9)

where SV₃₁ is the shape parameter of the front one of the two positive lenses.

The inequalities of condition (9) give a range for the shape of the above-identified positive lens to correct mainly decentering coma and decentering distortion well. When the convex curvature of the rear surface of that positive lens is stronger than the lower limit, the spherical aberration and the decentering coma become difficult to minimize. When it is stronger than the upper limit, the astigmatism and the decentering distortion become difficult to minimize.

It should be noted in connection with this embodiment that when the movable lens unit is decentered, a prism is generated and this prism produces chromatic aberrations. To reduce these aberrations as far as possible, or obtain good correction of chromatic aberrations over a wider range of wavelengths, it is required that the average values of the Abbe numbers of the media of the sets of positive lenses and negative lenses constituting the movable lens unit denoted by ν_(VP) and ν_(VN) respectively satisfy the following conditions:

    ν.sub.VP >45; ν.sub.VN <40                           (10)

When the condition (10) is violated, the entire area of the picture frame is largely stained with color, or the image quality is very badly lowered.

In this embodiment, it is possible to take the following constructional features

(i) The first and second lenses are constructed in the form of a cemented lens of two elements.

(ii) A filter or a fixed lens unit of weak power is used as arranged in rear of the movable lens unit.

(iii) At least one aspherical surface is used in the movable lens unit. In this case, when it is applied to the convex surface of the first lens, its shape is preferably figured such that the refractive power becomes progressively weaker toward the margin of the lens. When applied to the lens sub-unit, it is preferred that the refractive power becomes progressively stronger toward the margin. When the concave surface of the second lens is made aspherical, it is preferred to form it to such a shape that the negative refractive power becomes progressively stronger toward the margin.

(iv) As the decentering method of the movable lens unit, besides the parallel decentering tilting is performed.

(v) The lens unit behind the zoom section of a zoom lens is selected for the image stabilizing purpose

(vi) The principle of the invention is applied to objective lenses for observation, or the optical systems of surveying or measuring instruments.

The numerical data in accordance with which the examples 4-6 of this embodiment of the invention can be constructed are listed in the following tables for the radii of curvature, R, the axial thicknesses or air separations, D, and the refractive indices, N, and Abbe numbers, ν, of the glasses of the lenses with the subscription numbered from front to rear.

    __________________________________________________________________________     Numerical Example 4 (FIGS. 7, 8(A) and 8(B)):                                  F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 102.94                                                                             D1 = 19.43                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -478.84                                                                            D2 = 1.23                                                             R3 = 95.65                                                                              D3 = 19.13                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -261.16                                                                            D4 = 0.07                                                             R5 = -259.44                                                                            D5 = 5.63                                                                              N3 = 1.78590                                                                            ν3 = 44.2                                         R6 = 315.96                                                                             D6 = 0.51                                                             R7 = 57.52                                                                              D7 = 6.14                                                                              N4 = 1.60342                                                                            ν4 = 38.0                                   I     R8 = 46.90                                                                              D8 = 40.32                                                            R9 = -265.67                                                                            D9 = 6.14                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -74.81                                                                            D10 = 2.56                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 85.57                                                                             D11 = 29.12                                                           R12 = 615.62                                                                            D12 = 5.83                                                                             N7 = 1.59270                                                                            ν7 = 35.3                                         R13 = -57.12                                                                            D13 = 1.84                                                                             N8 = 1.80400                                                                            ν8 = 46.6                                         R14 = 199.96                                                                            D14 = 6.73                                                            R15 = 197.19                                                                            D15 = 4.30                                                                             N9 = 1.49700                                                                            ν9 = 81.6                                         R16 = -125.85                                                                           D16 = 2.79                                                            R17 = -45.39                                                                            D17 = 1.53                                                                             N10 = 1.63980                                                                           ν10 = 34.5                                        R18 = -1058.69                                                                          D18 = 13.53                                                     V     R19 = -163.69                                                                           D19 = 5.11                                                                             N11 = 1.69350                                                                           ν11 = 53.2                                        R20 = -51.78                                                                            D20 = 0.10                                                            R21 = 205.04                                                                            D21 = 4.09                                                                             N12 = 1.61800                                                                           ν12 = 63.4                                        R22 = -313.20                                                            __________________________________________________________________________

    __________________________________________________________________________     Numerical Example 5 (FIGS. 9, 10(A) and 10(B)):                                F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 97.88                                                                              D1 = 19.44                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -630.88                                                                            D2 = 1.23                                                             R3 = 94.95                                                                              D3 = 19.13                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -318.56                                                                            D4 = 1.14                                                             R5 = -284.75                                                                            D5 = 5.63                                                                              N3 = 1.78590                                                                            ν3 = 44.2                                         R6 = 305.84                                                                             D6 = 0.51                                                             R7 = 52.82                                                                              D7 = 6.14                                                                              N4 = 1.60342                                                                            ν4 = 38.0                                   I     R8 = 42.62                                                                              D8 = 39.76                                                            R9 = -353.43                                                                            D9 = 6.14                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -94.16                                                                            D10 = 2.56                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 80.70                                                                             D11 = 30.00                                                           R12 = 1142.13                                                                           D12 = 5.83                                                                             N7 = 1.59270                                                                            ν7 = 35.3                                         R13 = -52.75                                                                            D13 = 0.02                                                            R14 = -54.94                                                                            D14 = 2.05                                                                             N8 = 1.77250                                                                            ν8 = 49.6                                         R15 = 188.55                                                                            D15 = 6.74                                                            R16 = 149.91                                                                            D16 = 4.09                                                                             N9 = 1.49700                                                                            ν9 = 81.6                                         R17 = -147.38                                                                           D17 = 2.52                                                            R18 = -49.73                                                                            D18 = 1.53                                                                             N10 = 1.72047                                                                           ν10 = 34.7                                        R19 = -2047.48                                                                          D19 = 14.64                                                     V     R20 = -166.11                                                                           D20 = 5.11                                                                             N11 = 1.69680                                                                           ν11 = 55.5                                        R21 = -53.67                                                                            D21 = 0.10                                                            R22 = 174.48                                                                            D22 = 4.09                                                                             N12 = 1.61800                                                                           ν12 = 63.4                                        R23 = -292.28                                                            __________________________________________________________________________

    __________________________________________________________________________     Numerical Example 6 (FIGS. 11, 12(A) and 12(B)):                               F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________           R1 = 103.85                                                                             D1 = 19.43                                                                             N1 = 1.43387                                                                            ν1 = 95.1                                         R2 = -460.24                                                                            D2 = 1.23                                                             R3 = 97.53                                                                              D3 = 17.90                                                                             N2 = 1.49700                                                                            ν2 = 81.6                                         R4 = -290.78                                                                            D4 = 0.81                                                             R5 = -269.14                                                                            D5 = 5.63                                                                              N3 = 1.80610                                                                            ν3 = 40.9                                         R6 = 387.47                                                                             D6 = 10.60                                                            R7 = 50.65                                                                              D7 = 6.14                                                                              N4 = 1.58913                                                                            ν4 = 61.0                                   I     R8 = 41.76                                                                              D8 = 24.02                                                            R9 = -263.32                                                                            D9 = 6.14                                                                              N5 = 1.80518                                                                            ν5 = 25.4                                         R10 = -75.11                                                                            D10 = 2.56                                                                             N6 = 1.61340                                                                            ν6 = 43.8                                         R11 = 81.66                                                                             D11 = 29.72                                                           R12 = 320.07                                                                            D12 = 6.14                                                                             N7 = 1.58921                                                                            ν7 = 41.1                                         R13 = -61.63                                                                            D13 = 2.05                                                                             N8 = 1.81600                                                                            ν8 = 46.6                                         R14 = 177.28                                                                            D14 = 11.07                                                           R15 = 181.99                                                                            D15 = 3.58                                                                             N9 = 1.49700                                                                            ν9 = 81.6                                         R16 = -196.00                                                                           D16 = 4.87                                                            R17 = -45.99                                                                            D17 = 1.84                                                                             N10 = 1.76182                                                                           ν10 = 26.5                                        R18 = -252.61                                                                           D18 = 10.09                                                     V     R19 = -133.98                                                                           D19 = 5.11                                                                             N11 = 1.78590                                                                           ν11 = 44.2                                        R20 = -52.13                                                                            D20 = 0.10                                                            R21 = 257.84                                                                            D21 = 4.09                                                                             N12 = 1.59270                                                                           ν12 = 35.3                                        R22 = -176.36                                                            __________________________________________________________________________

Referring next to FIGS. 13 and 15, there is shown still another embodiment of the invention applied to a photographic lens of comparatively long focal length, wherein chromatic aberrations which are prominently produced when the lens is partly decentered are well corrected.

The photographic lens comprises, from front to rear, a fixed lens unit 1 in relation to the direction perpendicular to the optical axis, and a movable lens unit 2 upon movement in a direction perpendicular to the optical axis to compensate for the image blur. And, the movable lens unit 2 includes at least one positive and one negative lenses, satisfying the following conditions:

    75<.sub.p ν.sub.d                                       (11)

    0.525<.sub.P θ.sub.g,F <0.545                        (12)

where _(P) ν_(d) and _(P) θg,F are the Abbe number and partial dispersion ratio of the positive lens respectively (wherein the partial dispersion ratio θ_(g),F is defined by an equation: θ_(g),F =(n_(g) -n_(F))/(n_(F) -n_(C)) where n_(g), n_(F) and n_(C) are the refractive indices for the spectral g-line, F-line and C-line).

As has been described above, when the telephoto lens or like photographic lens of comparatively long focal length is partly decentered, various aberrations are produced. Of these, the decentering lateral chromatic aberration is very prominent, causing the image quality to lower. So, even if the movable lens unit 2 is corrected for usual two wavelengths in the not-decentered state, aberrations for the other wavelengths remain. When decentered, the remaining aberrations come to stand out, thus becoming another cause of lowering the image quality.

For this reason, in this embodiment, by satisfying the conditions (11) and (12), the remaining ones of the decentering lateral chromatic aberrations are corrected for good achromatization over the entire range of visible wavelengths. In addition, the responsiveness to the image blur is heightened. In more detail, the use of an extraordinary low dispersion optical material in the positive lens of the movable lens unit 2 provides a possibility of achromatizing the movable lens unit 2 itself by means of this positive lens of weak refractive power and the negative lens, giving an advantage that the thickness of the positive lens can be reduced. Therefore, its weight can be minimized.

Another advantage arising from the use of a larger Abbe number than 75 for the low dispersion of the positive lens is that, for the negative lens to be chosen on correction of chromatic aberrations, glass materials of relatively large Abbe number with a less amount of, for example, lead oxide contained become more liable to employ. It should be noted in this connection that if, as the percentage of lead oxide in the glass material is lower, the specific gravity can be reduced, the movable lens unit itself becomes lighter, contributing to an improvement of the responsiveness of the optical system.

Another advantage arising from the use of the lesser-lead oxide glass material in the negative lens is that the secondary spectrum can be reduced as compared with the case of using a lead oxide-rich glass material. As the optical material of large Abbe number mention may be made of fluorite. Its Abbe number is 95.15.

Next, the factor in the condition (12) represents the extraordinary dispersiveness of the optical material to be used in the positive lens of the movable lens unit. With the condition (11) being satisfied, when the condition (12) is satisfied as the partial dispersion ratio is larger than the lower limit, the variation with decentering of the remaining lateral chromatic aberrations can be minimized. Therefore, when decentering is carried out to compensate for the image blur, the resultant color blurring can be minimized. This feature can produce another advantage even at reduction of the secondary spectrum of the entire lens system. Optical materials exceeding the upper limit are, for now, hardly available.

The above-cited conditions suffice for accomplishing the objects of the invention. Yet, to achieve a further improvement of the aberration correction, it is preferred that the movable lens unit includes at least one negative lens, satisfying the following conditions:

    45>.sub.n ν.sub.d                                       (13)

    -0.012<.sub.n ν.sub.g,F -0.6438+0.001682·.sub.n ν.sub.d <-0.003                                                   (14)

where _(n) ν_(d) and _(n) θ_(g),F are the Abbe number and partial dispersion ratio of the negative lens respectively.

In connection with the factor in the condition (14), it should be explained that Schott Glaswerke, an optical glass maker of Germany, defines general normal glasses in terms of the relationship between the partial dispersion ratio θ_(g),F and the Abbe number νd as assumed to lie on a line connecting two glasses K7 and F2. This line is expressed by an equation: θ_(g),F =0.6438-0.001682·ν_(d). What is called the extraordinary dispersiveness means a large deviation from this straight line. The larger the deviation, the higher the extraordinary dispersiveness.

The inequalities of conditions (13) and (14) represent a range for choice of such a lens to be used in the negative lens of the movable lens unit to correct chromatic aberrations and further to heighten the effect described in connection with the condition (12). The condition (13) is for correction of the chromatic aberrations of the movable lens unit. When it is violated, the amount of chromatic aberrations produced by decentering is increased somewhat objectionably. The factor in the condition (14) represents a range for the deviation of the partial dispersion ratio of that negative lens from that of the normal glass. When the upper limit is exceeded, the above-described further improvement cannot be so much expected. What exceeds the lower limit is hardly amenable to the glass manufacture techniques.

And, it is more preferable to satisfy the following additional condition:

    0.3f.sub.T <f.sub.X <0.7f.sub.T                            (15)

where f_(X) is the focal length of the positive lens, and f_(T) is the focal length of the entire lens system.

The inequalities of condition (15) represent a range for the focal length of the positive lens that satisfies the conditions (11) and (12). When the focal length is chosen so short as not to exceed the upper limit, the advantage of the lens having the extraordinary dispersion described in connection with the conditions (11) and (12) can fully be produced. When the lower limit is exceeded, the spherical aberration and coma are increased largely. The annular aberration is also increased objectionably. It is also preferred that within the framework of the condition (12), the movable lens unit further includes a second positive lens, satisfying the following condition:

    0.003<.sub.n2 θ.sub.g,F -0.6438+0.001682·.sub.n2 νd<0.012(16)

where _(n2) ν_(d) and _(n2) θg,F are the Abbe number and the partial dispersion ratio of the second positive lens respectively.

The inequalities of condition (16) are to assist in promoting the effect described in connection with the condition (12), and, for this purpose, limits a range for the choice of optical materials to be used in the other positive lens. When the condition (16) is satisfied as the deviation of the partial dispersion ratio from that of the normal glass is larger than the lower limit, a surplus effect can be produced.

What exceeds the upper limit is hardly amenable to the glass manufacture techniques.

It should be pointed out that in order to assure the promotion of the effect of the extraordinary dispersion, the positive lenses are arranged in the frontmost position within the movable lens unit, because the height of the paraxial, on-axial ray of light is relatively high at that position.

Two numerical examples 7 and 8 of the embodiments shown in FIGS. 13 and 15 can be constructed in accordance with the numerical data given in the following tables for the radii of curvature, R, the axial thicknesses or air separations, D, and the refractive indices, N, and Abbe numbers, ν, of the glasses of the lens elements with the subscription numbered from front to rear.

The values of the aberration coefficients for the numerical example 7 are listed in Table 1.

In this example, the frontmost positive lens in the movable lens unit is made up from a low-dispersion optical material having such an extraordinary dispersiveness that the Abbe number is 81.6 and the partial dispersion ratio θ_(g),F is 0.537 so that the variation with decentering of the remaining lateral chromatic aberrations over the entire visible wavelength range is corrected to a minimum. Also, since the glass of very low dispersive power is used in the positive lens, the second negative lens may be made up of an Abbe number of 34.7 or a glass of lighter weight due to the lesser amount of contained lead. Therefore, the weight of the movable lens unit is reduced, contributing to an excellent responsiveness of driving operation of the actuator. Also, since a glass of relative low refractive index may be selected for employment in the negative lens, the Petzval sum of the movable lens unit can be reduced in order to minimize the decentering field curvature and decentering distortion.

Again, in the numerical example 7, the rearmost positive lens in the movable lens unit is made up of an Abbe number of 63.38 and a partial dispersion ratio θ_(g),F of 0.5439, or an optical glass having such an extraordinary dispersiveness that the deviation of the ratio θ_(g),F from that of the normal glass is 0.0067 to thereby heighten the above-described effect.

The numerical example 8 is similar to the example 7 in that the optical material of 81.6 in Abbe number add 0.537 in partial desperation ratio θ_(g),F is used in the frontmost positive lens in the movable lens unit, but different therefrom in that even the second negative lens is made up also by using an optical material of 4.72 in Abbe number and 0.5821 in the partial dispersion ratio θ_(g),F with such an extraordinary dispersiveness that the deviation of the ratio θ_(g),F from that of the normal glass is -0.0033 to heighten the effect.

    __________________________________________________________________________     Numerical Example 7 (FIGS. 13, 14(A) and 14(B)):                               F = 300 FNo = 1:2.8 2ω = 8.25°                                    __________________________________________________________________________         R1 = 102.948                                                                            D1 = 19.43                                                                            N1 = 1.43387                                                                           ν1 = 95.1                                           R2 = -478.847                                                                           D2 = 1.23                                                             R3 = 95.657                                                                             D3 = 19.13                                                                            N2 = 1.49700                                                                           ν2 = 81.6                                           R4 = -261.164                                                                           D4 = 0.07                                                             R5 = -259.449                                                                           D5 = 5.63                                                                             N3 = 1.78590                                                                           ν3 = 44.2                                           R6 = 315.966                                                                            D6 = 0.51                                                             R7 = 57.523                                                                             D7 = 6.14                                                                             N4 = 1.60342                                                                           ν4 = 38.0                                       1   R8 = 46.904                                                                             D8 = 40.32                                                            R9 = -265.672                                                                           D9 = 6.14                                                                             N5 = 1.80518                                                                           ν5 = 25.4                                           R10 = -74.817                                                                           D10 = 2.56                                                                            N6 = 1.61340                                                                           ν6 = 43.8                                           R11 =  85.577                                                                           D11 = 29.12                                                           R12 = 615.626                                                                           D12 = 5.83                                                                            N7 = 1.59270                                                                           ν7 = 35.3                                           R13 = -57.124                                                                           D13 = 1.84                                                                            N8 = 1.80400                                                                           ν8 = 46.6                                           R14 = 199.967                                                                           D14 = 6.73                                                            R15 = 197.196                                                                           D15 = 4.30                                                                            N9 = 1.49700                                                                           ν9 = 81.6                                                                         Q.sub.g, F = 0.537                               R16 = -125.854                                                                          D16 = 2.79                                                            R17 = -45.398                                                                           D17 = 1.53                                                                            N10 = 1.63980                                                                          ν10 = 34.5                                          R18 = -1058.691                                                                         D18 = 13.53                                                       2   R19 = -163.692                                                                          D19 = 5.11                                                                            N11 = 1.69350                                                                          ν11 = 53.2                                          R20 = -51.783                                                                           D20 = 0.10                                                            R21 = 205.049                                                                           D21 = 4.09                                                                            N12 = 1.61800                                                                          ν12 = 63.4                                                                        Q.sub.g, F = 0.5439                              R22 = -313.203                                                             __________________________________________________________________________

                                      2                                            __________________________________________________________________________     Numerical Example 8 (FIGS. 13, 14(A) and 14(B)):                               F = 300 FNo = 1:2.8  2ω = 8.25                                           __________________________________________________________________________         R1 = 97.887                                                                             D 1 = 19.44                                                                           N1 = 1.43387                                                                           ν1 = 95.1                                           R2 = -630.887                                                                           D2 = 1.23                                                             R3 = 94.959                                                                             D3 = 19.13                                                                            N2 = 1.49700                                                                           ν2 = 81.6                                           R4 = -318.567                                                                           D4 = 1.14                                                             R5 = -284.750                                                                           D5 = 5.63                                                                             N3 = 1.78590                                                                           ν3 = 44.2                                           R6 = 305.849                                                                            D6 = 0.51                                                             R7 = 52.820                                                                             D7 = 6.14                                                                             N4 = 1.60342                                                                           ν4 = 38.0                                       1   R8 = 42.628                                                                             D8 = 39.76                                                            R9 = -353.438                                                                           D9 = 6.14                                                                             N5 = 1.80518                                                                           ν5 = 25.4                                           R10 = -94.167                                                                           D10 = 2.56                                                                            N6 = 1.61340                                                                           ν6 = 43.8                                           R11 = 80.700                                                                            D11 = 30.00                                                           R12 = 1142.134                                                                          D12 = 5.63                                                                            N7 = 1.59270                                                                           ν7 = 35.3                                           R13 = -52.757                                                                           D13 = 0.02                                                            R14 = -54.948                                                                           D14 = 2.05                                                                            N8 = 1.77250                                                                           ν8 = 49.6                                           R15 = 188.555                                                                           D15 = 6.74                                                            R16 = 149.911                                                                           D16 = 4.09                                                                            N9 = 1.49700                                                                           ν9 = 81.6                                                                         Q.sub.g, F = 0.537                               R17 = -147.385                                                                          D17 = 2.52                                                            R18 = -49.738                                                                           D18 = 1.53                                                                            N10 = 1.72047                                                                          ν10 = 34.7                                                                        Q.sub.g, F = 0.5821                              R19 = -2047.488                                                                         D19 = 14.64                                                       2   R20 = -166.119                                                                          D20 = 5.11                                                                            N11 = 1.69680                                                                          ν11 = 55.5                                          R21 = -53.675                                                                           D21 = 0.10                                                            R22 = 174.489                                                                           D22 = 4.09                                                                            N12 = 1.161800                                                                         ν12 = 63.4                                                                        Q.sub.g, F =  0.5439                             R23 = -292.281                                                             __________________________________________________________________________

                  TABLE 1                                                          ______________________________________                                         (Aberration coefficients of numerical example 7)                               ______________________________________                                         NO-NO  L          T         SA       CM                                        ______________________________________                                         1 - 1  0.011422   -0.009604 5.222094 -4.390883                                 2      0.007803   -0.012784 3.806683 -6.236865                                 3      0.006649   -0.002513 -0.358436                                                                               0.135477                                  4      0.017740   -0.024085 32.715652                                                                               -44.418106                                5      -0.044602  0.060538  -40.223434                                                                              54.594879                                 6      0.013606   -0.026993 1.908904 -3.787021                                 7      0.019042   -0.007376 -1.002450                                                                               0.388305                                  8      -0.025592  0.013705  0.108220 -0.057954                                 9      -0.025852  0.039762  -3.587972                                                                               5.518496                                  10     0.026602   -0.027922 2.470170 -2.592738                                 11     -0.004172  -0.008599 0.027208 0.056082                                  12     -0.002919  0.013719  -0.048575                                                                               0.228272                                  13     0.002476   -0.001481 -1.155621                                                                               0.691090                                  14     -0.002447  -0.012297 -0.015356                                                                               -0.077158                                 15     0.001034   0.005297  0.014375 0.073624                                  16     0.002901   -0.004000 0.538584 -0.742663                                 17     -0.016229  0.007853  -3.455609                                                                               1.672156                                  18     -0.003382  -0.016153 -0.064960                                                                               -0.310235                                 19     0.000064   0.009620  0.000035 0.005227                                  20     0.010746   -0.000745 2.560075 -0.177552                                 21     0.000614   0.007978  -0.001706                                                                               -0.022178                                 22     0.004146   -0.003844 0.544242 -0.504575                                 1 - 22 -0.000353  0.000077  0.002110 0.045688                                  ______________________________________                                         NO-NO    AS         PT          DS                                             ______________________________________                                         1 - 1    3.691978    0.881762   -3.845730                                      2        10.218473  0.189572    -17.052521                                     3        -0.051206  1.041216    -0.374192                                      4        60.306549  0.381366    -82.396118                                     5        -74.101105 -0.508837   101.267349                                     6        7.512962   -0.417821   -14.075848                                     7        -0.150412  1.962699    -0.702000                                      8        0.031035   -2.407029   1.272385                                       9        -8.487747  -0.503673   13.829294                                      10       2.721389   0.264035    -3.133559                                      11       0.115597   -1.332800   -2.508936                                      12       -1.072728  0.181345    4.188915                                       13       -0.413289  -0.386219   0.478126                                       14       -0.387683  -0.668623   -5.307459                                      15       0.377095   0.505076    4.518367                                       16       1.024071   0.791385    -2.503364                                      17       -0.89150   -2.578347   1.639197                                       18       -1.481619  0.110562    -6.547897                                      19       0.786315   -0.750509   5.386514                                       20       0.012314   2.372428    -0.165392                                      21       -0.288296  0.558821    3.516590                                       22       0.467800   0.365852    -0.772892                                      1 - 22   0.022347   0.052261    -3.289181                                      ______________________________________                                          L: Lateral chromatic aberration coefficient                                    T: longitudianal chromatic aberration coefficient                              SA: spherical abberration coefficient                                          CM: coma aberration coefficient                                                AS: astigmatism coefficient                                                    PT: Petzval sum                                                                DS: distortion coefficient                                               

By the way, in the foregoing embodiments, of the two main aspects of the optical performance, discussion has been conducted from the aberrational standpoint.

In the following, from another standpoint, how to preserve the other aspect of the optical performance at excellent throughout the decentering range will be described, pointing out what problems arise.

FIGS. 18(A) and 18(B) diagrammatically illustrate the effect of perpendicular movement of the movable lens unit V to the optical axis on the compensation for, say, the image blur, and are taken to explain how the off-axial ray (to an image height y=±18 mm at the focal plane) and the on-axial ray (y=0) change their paths when the movable lens unit V moves 7 mm in an upward direction perpendicular to the optical axis from the start position of FIG. 18(A) to a decentered position of FIG. 18(B).

As show here, when the movable lens unit V is decentered upwardly or to a positive direction, the illumination increases in the place where the image height is of plus sign, while, in the place of image height of minus sign, the illumination decreases to a greater extent. Thus, a very large difference in image illumination between the upper and lower halves of the area of the picture frame results, or the uniformity of illumination over the entire area of the picture frame is broken.

This is because, for the image height of minus sign (the lower half of the picture frame), the effective diameter of the movable lens unit V trims the effective diameter of the fixed lens unit I fixed in the vertical direction relative to the optical axis to reduce the intensity of the off-axial light beam, and the apparent field angle for the light beam, even though being to reach the same image height in the lower half of the picture frame, is widened to reduce the intensity of that light beam by the prism effect due to the decentering of the movable lens unit V.

That is, the disagreement between the effective diameters of the two lens units V and I hardly affects the illumination at the image height of plus sign (the upper half of the picture frame). Moreover, because the light beam, though being to reach the same image height at the focal plane in the upper half of the picture frame, has its apparent field angle narrowed by that prism, surplus rays of light are admitted to pass.

FIGS. 19 and 20 illustrate the variations of the aperture efficiency with the image height in the start and 5 mm decentered positions of FIGS. 18(A) and 18(B) respectively. FIGS. 21 and 22 illustrate the aberrations in the start and the decentered positions respectively.

As shown in FIG. 20, there is a phenomenon of intensifying the uneven distribution of illumination intensity over the marginal zone of the picture frame. If the effective diameter of each of the fixed and movable lens units I and V is larger than enough, this phenomenon can no logger take place. However, if it were made so, the bulk and size of the lens would become very large, and the good manageability would be broken. As a general rule, therefore, the effective diameter is made minimum.

With this, when the movable lens unit V is decentered 5 mm to compensate for the image blur, it admits for abnormally increased rays of light to reach the image heights of plus sign (the upper half of the picture frame) as shown in FIG. 20. Such surplus rays of light behave as a flare as shown in FIG. 22, causing the image quality to be lowered largely.

Hence, from here onward, an embodiment of the invention is described that enables such a flare to be reduced or eliminated.

FIG. 17 is a schematic diagram of an optical system to which this embodiment is applied. In this figure, there is shown a case of compensating for the image blur by using a movable lens unit V. In the illustrated position of this figure, the movable lens unit V has moved from the start position by a predetermined distance to stabilize the image. A is the above-described acceleration detecting device; B is driving means for moving the lens unit V; and D is a device for driving a diaphragm to move as shown by arrows on the basis of the output of the acceleration detecting device A.

The photographic lens of this embodiment has a focal length f=300 mm, and an F-number of F2.8 at full open aperture. In the figure, I is the fixed lens unit; V is the movable lens unit upon parallel decentering movement in a direction perpendicular to the optical axis to compensate for the image blur. P is a light beam limiting member provided in separation from the diaphragm (not shown) that determines F-numbers.

In this embodiment, the image blur is detected by an image blur detecting means (not shown). The movable lens unit V is made parallel decentered by an actuator (not shown) in a direction perpendicular to the optical axis to so predetermined a distance as to compensate for that image blur. The same figure shows the case when the movable lens unit V has been parallel decentered 5 mm in a direction perpendicular to the optical axis. By this, the image is shifted about 5 mm on the focal plane.

And, a lowering of the optical performance due particularly to the flare caused by the various aberrations shown in FIG. 22 due to the unevenness of the illumination intensity distribution of the marginal portion of the image frame as shown in FIG. 20 when the movable lens unit has been parallel decentered, is corrected by using the light beam limiting member P having a round opening as shown in FIG. 23.

That is, as shown in FIG. 17, the beam limiting member P is provided near or within the movable lens unit V, and is made to move in the reverse direction to that in which the movable lens unit V moves so that one side of the beam is shut off to improve the illumination intensity distribution as shown in FIG. 24. FIG. 25 is a graphic representation of the aberrations at this time.

In such a manner, the lowering of the optical performance caused to occur when the image blur is compensated for by causing the movable lens unit V to move is corrected by using the beam limiting member P. This constitutes a feature of this embodiment.

In this embodiment, the beam limiting member may be arranged anywhere within the photographic lens provided the light beam to the margin of the picture frame can be partly shut off in that position, for example, any one of positions a, b, c and d shown in FIG. 17.

The direction of movement of the beam limiting member changes in various ways depending on the value of the refractive power of the movable lens unit, but, in principle, it may be moved to such a direction as to block the unnecessary light beam, and no particular definition should be laid.

For example, in this embodiment, because the movable lens unit is of positive power, the direction of movement of the member P is made opposite to that of movement of the movable lens unit. If it is of negative power, the member P must be move in the same direction as that of movement of the lens unit V. If so, the object of the invention can be accomplished well.

The shape of the opening of the beam limiting member is not limited to the round one, but may be modified to a desired one such as ellipse or elongated circle.

Also, instead of the mechanical means having an opening portion of fixed size, electrical means may be used to vary the size of the pass opening for the light beam to be restricted. The transmittance in the pass opening is varied as in, for example, a liquid crystal, electrochromic (EC) or like element. And, this element as the beam limiting member is made to move.

The movement of the movable lens unit and the beam limiting member is not limited to the direction perpendicular to the optical axis, but may be in an oblique direction to the optical axis so that not only the image is stabilized, but also the illumination intensity distribution and all aberrations over the entire area of the picture frame are corrected.

According t this, the image blur and the aberration can be corrected in better balance.

It should be noted that, in this embodiment, it is preferred that the beam limiting member is positioned on the image side of the aperture stop of the photographic lens, because the various aberrations when the beam limiting member is moved can be corrected in good balance.

In this embodiment, the case of moving the movable lens unit in the direction perpendicular to the optical axis to compensate for the image blur has been illustrated. It is of course possible to apply the invention to other cases when the movable lens unit is used in vibration-proof, shift photography, automatic tracing, or in achieving the above-described aims.

According to the present invention, a photographic lens having a plurality of lens units is provided with means making it possible to alter the optical characteristics as required when the image is stabilized against accidental vibratory motion or shift photography is carried out, by decentering one of the lens units in a direction perpendicular to the optical axis, while still permitting uniform illumination intensity distribution over the entire area of the picture frame to be always obtained, and further a good stability of the image quality to be achieved over the entire decentering range. 

What is claimed is:
 1. An optical system for correcting image blurring comprising, from front to rear, a fixed lens unit stationary relative to a direction perpendicular to the optical axis, and a movable lens unit with means for moving said movable lens unit in a direction having a directional component transverse to the optical axis to stabilize an image, said movable lens unit including a plurality of lenses, and satisfying the following condition:

    0.05<L.sub.2 /F <0.4

where L₂ is the length from a frontmost lens surface in said movable lens unit to a rearmost lens surface therein, and F is the focal length of the entire lens system.
 2. A photographic optical system according to claim 1, wherein said movable lens unit includes a front lens sub-unit and a rear lens sub-unit with a longest air separation therebetween, satisfying the following conditions:

    0.05<D.sub.max ·φ.sub.II <0.6

    0.4<φ.sub.IIB /φ.sub.II <2

where D_(max) is said air separation, and φ_(II) and φ_(IIB) are the refractive powers of said movable lens unit and said rear lens sub-unit, respectively.
 3. A photographic optical system according to claim 1 or 2, satisfying the following condition:
 0. 1<R_(IIa) /F<0.6where R_(IIa) is the radius of curvature of the frontmost lens surface in said movable lens unit.
 4. A photographic optical system according to claim 2, wherein said front lens sub-unit includes at least one positive lens and a negative lens, and wherein said rear lens sub-unit includes at least one positive lens.
 5. A photographic optical system according to claim 1, wherein said movable lens unit includes a positive first lens, a negative second lens having a strong negative refracting surface on the object side as compared with the image side, and a positive third lens, and wherein letting the focal length of the entire lens system be denoted by F, the focal length and the total lens length of said movable lens unit by FV and L2, respective, and air separation between said first lens and said second lens by DV₁₂, and the shape parameters of said first lens and said second lens by SV₁ and SV₂, respectively, where the shape parameter S is defined by S=(RB+RA)/((RB-RA) wherein RA and RB represent the radii o curvature of the front and rear surfaces of a lens, the following conditions are satisfied:

    0.05<L2/F<0.2

    -2<SV.sub.1 <1

    0<SV.sub.2 >5

    0.01<DV.sub.12 /FV<0.08.


6. A photographic optical system according to claim 5, wherein said lens sub-unit includes at least two positive lenses, satisfying the following condition:

    -5<SV.sub.31 <-0.5

where SV₃₁ is the shape parameter of the one of said positive lenses which is positioned on the object side.
 7. A photographic optical system according to claim 5 or 6, satisfying the following conditions:

    ν.sub.VP >45

    ν.sub.VN <40

where ν_(VP) and ν_(VN) are the average values of the Abbe numbers of the media of the positive lenses and negative lenses constituting said movable lens unit, respectively.
 8. A photographic lens system according to claim 1, wherein said means for moving further comprises detection means for detecting blurring of the image and drives said movable lens unit on the basis of an output of said detection means.
 9. A photographic optical system comprising a fixed lens unit stationary relative to a direction perpendicular to the optical axis, and a movable lens unit arranged on the image side of said fixed lens unit with means for moving said movable lens unit in a direction having a directional component transverse to the optical axis to deflect an image, said movable lens unit including a positive lens and a negative lens, and satisfying the following condition:

    .sub.pν.sub.d >75

    0.525<.sub.p θ.sub.g,F <0.545

where _(p) θ_(d) and _(p) θ_(g),F are the Abbe number and the partial dispersion ratio of said positive lens respectively, wherein a partial dispersion ration θ_(g),F is defined by an equation: θ_(g),f =(n_(g) -n_(F))/(n_(F) -n_(C)) wherein n_(g), n_(F) and n_(C) are the refractive indices for the spectral g-line, F-line and C-line, respectively.
 10. A photographic optical system according to claim 9, satisfying the following conditions:

    45>.sub.n ν.sub.d

    -0.012<.sub.n θ.sub.g,F -0.6438+0.001682·.sub.n θ.sub.d <-0.003

where _(n) νd and _(n) θ_(g),F are the Abbe number and the partial dispersion ratio of said negative lens of said movable lens unit, respectively.
 11. A photographic optical system according to claim 9, satisfying the following condition:

    0.3f.sub.T <f.sub.x <0.7f.sub.T

wherein f_(x) is the focal length of said positive lens, and f_(T) is the focal length of the entire lens system.
 12. A photographic lens system according to claim 11, wherein said means for moving further comprises a detecting unit for detecting blurring of an image, and moves said movable lens unit and said light limiting means on the basis of an output of said detecting means.
 13. A photographic optical system according to claim 9, wherein said movable lens unit further includes a second positive lens, satisfying the following condition:

    0.003<.sub.n2 θ.sub.g,F -0.6438+0.001682·.sub.n2 ν.sub.d <0.012

where _(n2) ν_(d) and _(n2) θ_(g),F are the Abbe number and the partial dispersion ratio of said second positive lens, respectively.
 14. A photographic lens having an optical axis, comprising a movable lens unit and means for moving said movable lens unit in a direction having a directional component transverse to the optical axis to deflect an image, and light limiting means movable in a direction perpendicular to the optical axis in synchronism with movement of said movable lens unit and having a limiting portion for limiting light.
 15. A photographic lens according to claim 14, wherein said limiting portion is constructed from an element whose transmittance varies electrically.
 16. A photographic lens according to claim 15, wherein said element is a liquid crystal. 